To Örebro University

Green liquor dreg (GLD) is a calcite dominated alkaline byproduct from the pulp and paper industry with high buffering capacity and thixotropic properties, making it suitable for treatment of acidic mining waste. In a comprehensive four-year study, GLD from 16 Swedish mills was characterised through multiple sampling campaigns, analysing elemental composition, buffering capacity, sequential leaching, and interactions with acid rock drainage. This dataset is now a robust foundation for understanding the variability of GLD between mills, offering key insights into which parameters are most critical for different mining waste applications.

Several small and medium sized tests have been performed, with good results, to determine the suitability and possible drawbacks when mixing GLD and acid mining waste. As a final confirmation of the technique approximately 4,500 tonnes of acid mining waste at Gladhammar, Sweden (pH 3.8, 96 mg/L copper and 21 mg/L cobalt) was slurry injected with 100 tonnes of GLD in 2017.

During injection, pH in the drainage from the area increased from 3.5 to around 10 due to excess GLD being washed out. One to two months after injection, pH was around 7.5 and concentrations of copper and cobalt was 38 and 4.9 mg/L, respectively. During 2024, pH was 8 and concentrations of copper and cobalt were 1.1 and 0.95 mg/l, respectively.

The challenge at Gladhammar was to reduce metal loads while allowing the waste rock piles to be accessible for mineral hunters and geoscientific studies in the future. With alkaline injections, areas with cultural, historical and geological values can be treated with low visual impact.

The full-scale reclamation at Gladhammar confirms that GLD can be used for reclamation of historical mining waste as pH increases and trace element concentrations decrease. 

Green liquor dregs (GLD) is an alkaline by-product from the pulp and paper industry with a pH between 10 and 14. Today most of the produced GLD in Sweden is landfilled. As a fine-grained alkaline material, it might be possible to use it for acid-generating mining waste remediation. To increase the utilization, quality characteristics and environmental performance need to be determined. In this study samples were collected 5 times from 16 mills during a period of 2.5 years, and were characterized by analyzing dry matter content, loss on ignition (LOI) 550 °C and LOI 950 °C, elemental analysis, pH, electrical conductivity, and calorific value. The results were then evaluated using multivariate statistics (PCA) as well as being compared to other studies and Swedish till. The results show that even if GLD is heterogenous (both within a mill and between different mills) trends can be seen for samples from most mills. When samples do stand out, it is predominately related to the same four mills. Most of the studied parameters showed characteristics favorable for use as a remediant; however, TOC, sulfur, and some of the elements require further study. In general, this study concludes that GLD can be a viable option for the remediation of small orphaned sulfidic mining sites and thus worthy of further studies on the interaction between GLD and acidic mining waste.Overall, GLD can be a good alternative for cost-effective remediation of smaller orphaned mining sites. It is readily available in large quantities, has the qualities needed for remediation of many orphaned acidic mining sites, and can often be locally sourced near the mining site. The use of GLD for mining site remediation is likely also a more sustainable method compared to traditional remediation methods.

It is difficult to evaluate the potential for reprocessing and extraction of minerals from waste rock with valuable and/or harmful elements.

We suggest a new sampling strategy/protocol for waste rock, specifically developed for historic mining sites, in combination with XRF-XRT scanning with a GeoCore X10 instrument.

Håkansboda historical mine site in Sweden was used as a case study to look at the potential for the combination of techniques.

The combination of the suggested randomized sampling strategy/protocol and the dataset from the GX10 scanning enables prediction of amenability for pre-processing with the use of mechanical sorting or if the extraction of valuable minerals only can be achieved through fine grinding, flotation or leaching.

Green liquor dregs (GLD) is an alkaline by-product from the paper and pulp industry with a pH between 10 and 14. Today most of the produced GLD in Sweden are landfilled. In order to increase the utilization, the environmental performance needs to be determined. Samples were collected from 16 mills at 3 different times approximately 6 months apart, totalling 42 samples. Leaching was performed in two sequential steps at an L/S ratio of 2 and 8 on wet samples corresponding to 25 g DM. The liquid phases were analysed for pH, electrical conductivity, alkalinity, anions and element concentrations. Leaching of sodium and potassium were as expected very high but leaching of calcium was low. Chromium, nickel, copper, cadmium and zinc leaches generally less than ≤5% of total concentrations. Sodium and potassium are present in GLD as easily soluble salts that are easily washed out. Calcium leaching is restricted by calcite solubility resulting in little effect on short time buffering capacity, however, in the long term calcium minerals will affect the buffering capacity. For nickel, copper, cadmium and lead there are some soluble salts present in the GLD but most of the elements are probably solubility controlled. Geochemical calculations indicated hydroxides as solubility controlling phases for at least copper and in some cases also for lead. Leaching of zinc is to some extent solubility controlled which is indicated by the fact that the soluble concentrations is similar for both L/S 2 and L/S 8. When comparing the leached concentrations from GLD with concentrations from mining waste there is an environmental benefit even if the GLD is not inert. In conclusion, GLD is well suited to be used for treatment of acidic mining waste instead of being landfilled in non-hazardous and hazardous landfills.

Mining in Gladhammar, southern Sweden started in the 15th century, generating waste rock containing copper, cobalt, and arsenic. During remediation (2011) some waste rock was preserved, due to its geoscienti- c value, and placed on a geomembrane surface. Eventually, it became apparent that it had a substantial environmental impact (pH 3.8, Cu 96 mg/L, Co 21 mg/L). In 2017, green liquor dregs was injected in order to increase pH and decrease trace element mobility. Ten months a er injection pH was 8.3 and concentrations of copper and cobalt 1.3 mg/L and 1.1 mg/L, respectively. Evaluation will continue for at least five years.

Mining has been and still is an important industry in Sweden. Leaching from sulfidic mining waste is however a serious environmental issue that can bring acidity and metals in solution. Simultaneously, green liquor dreg (GLD) with potential to decrease oxygen transport to the waste and neutralize acid leachate, is generated by the pulp and paper industry and deposited in landfills. The aim of the project is to promote valorisation of GLD, identify hinders and create a database providing information about the material and its variability to enhance establishment of circular economy for the pulp and paper mill waste.

There is today no overall information about how much mining waste there is in Sweden and what it contains. This project focused on samples from waste rock, tailings and slag from the historical mining region Bergslagen, Sweden. Modern dissolution and analytical methods were used in order to determine approximately 50 elements in the samples. Modern analytical data for the historical mining waste is useful as an exploration tool and can provide information about remaining or new resources underground. Results show that there is a potential for recovery of critical elements from mining waste as well as dealing with environmental problems.

ARD from historical mining sites in Sweden is a major source for trace elements to surface waters. In order to be able to treat a large portion of these sites cost effective reclamation methods is necessary. Incineration ashes were used in leaching tests to study their effect on a highly weathered mining waste in order to neutralize acidity and immobilize trace elements. This study shows that ashes can be used to increase pH and decrease trace element mobility from oxidized mining waste. Increased leaching of Cl, Mo and Sb, however, needs to be considered for waste fuel ashes before use.

Due to oil production from alum shale, the Kvarntorp area is heavily polluted. A waste deposit consisting mostly of shale ash and fines is of important concern. Groundwater shows that parameters such as pH, U, V, Ni and Mo are different at different localities around the deposit. Leaching tests indicate that burned and unburned shale residues leave different signatures on leachates. Principal component analysis of groundwater and leaching tests suggest that ground-water is affected by the waste deposit and that it is more influenced by shale ash than by fines.

Due to oil production from alum shale, the Kvarntorp area is heavily polluted. A waste deposit consisting mostly of shale ash and fines is of important concern. Groundwater shows that parameters such as pH, U, V, Ni and Mo are different at different localities around the deposit. Leaching tests indicate that burned and unburned shale residues leave different signatures on leachates. Principal component analysis of groundwater and leaching tests suggest that ground-water is affected by the waste deposit and that it is more influenced by shale ash than by fines.